Modernize en Optimize (A LOT) PHP platform

* Use an external file to be able to run static analysis tool (ATM,
  analyzer crash because the file is too big)
* Enable the opcache caching feature (better for the RAM)
* Use key instead of value when searching in the array
* Add type hint everywhere
* Use generator to lazy load evualuation as much as possible

composer.json

@@ -1,8 +1,11 @@
 {
     "name": "fgribreau/mailchecker",
     "description": "Temporary (disposable/throwaway) email detection library. Covers 1987 fake email providers.",
-    "keywords": ["fake", "email", "detection"],
+    "keywords": ["fake", "email", "detection", "disposable"],
     "license": "MIT",
+    "require": {
+        "php": ">=7.3"
+    },
     "require-dev": {
         "phpunit/phpunit": "^7.0"
     },